The present invention relates to a process for controlling the shape of a workpiece surface machined by a travelling electrode wire and to an EDM apparatus for practicing the method.
Known methods for detecting machining errors in the course of cutting a workpiece in a travelling wire EDM apparatus, by means of an electrode wire, such known methods consisting in measuring the deviation of the electrode wire relative to a straight line drawn between the electrode wire guide members, either by a direct measurement of the deviation between the workpiece and one of the electrode wire guides, or with respect to the motion of the electrode wire guides relative to the workpiece. The deviation of the wire causes an error in the cutting path or causes a convex or concave surface to be machined on the workpiece when a finish machining operation is effected.
In addition, other machining surface defects can appear on the machined surface even though the electrode wire may be drawn rectilinear between its guides. One of the causes for such surface defects is due to variations in the pollution rate of the dielectric fluid along the machining zone, whose effect it is to vary in turn the machining gap between the electrode wire and the workpiece surface as a direct function of the pollution rate. Another cause for such surface defects is due to dirt or other debris adhering to the workpiece at some portions of the machining zone. The known methods for detecting machining errors are not capable of detecting surface defects and are therefore not capable of avoiding such defects by way of an adequate modification of the machining conditions.